The present invention relates to a reduction-drive device used to such as a four wheel drive automobile.
As a conventional reduction-drive device, there is, for example, a device as shown in FIG. 15. The reduction-drive device 201 of FIG. 15 reduces an output of an electric motor 203 to transmit to left and right axle shafts and drive the left and right rear wheels. The electric motor 203 is served as a sub-drive source, and at a side of front wheels, an engine is served as a main drive source, and the left and right front wheels are driven by the engine.
The motor reduction-drive device 201 rotatably supports a first transmission shaft 207, that receives an output of the electric motor 203, at a housing 205 of a stationary side. The first transmission shaft 207 has a reduction gear 211 composing a first reduction mechanism 209. The reduction gear 211 is in mesh with another reduction gear 213 composing the first reduction mechanism 209. The reduction gear 213 is provided to a second transmission shaft 215. The second transmission shaft 215 is disposed in parallel to the first transmission shaft 207, and is rotatably supported to the housing 205.
The second transmission shaft 215 is provided with a reduction gear 219 composing a second reduction mechanism 217. The reduction gear 219 is in mesh with another reduction gear 221 of the second reduction mechanism 217. The reduction gear 221 of the second reduction mechanism 217 is provided to a third transmission shaft 223. The third transmission shaft 223 is disposed in parallel to the first and second transmission shafts 207, 213 and is rotatably supported to the housing 205.
The third transmission shaft 223 is provided with a reduction gear 227 composing a third reduction mechanism 225. The reduction gear 227 is in mesh with a ring gear 229 as another reduction gear of the third reduction mechanism 225. The ring gear 229 is provided to a rear differential 231 as a differential device. A rotating shaft of the rear differential 231 is disposed in parallel to the first, second, third transmission shafts 209, 215, 223. The rear differential 231 is connected in interlocking with the left and right rear wheels via axle shafts.
Accordingly, by driving of the electric motor 203, the first transmission shaft 207 is driven to transmit torque to the second transmission shaft 215 via the first reduction mechanism 209. From the second transmission shaft 215, via the second reduction mechanism 217, the torque is transmitted to the third transmission shaft 223, and is transmitted to the rear differential 231 via the third reduction mechanism 225. From the rear differential 231, via the left and right axle shafts, the torque is transmitted to the left and right rear wheels, and the left and right rear wheels are driven by the electric motor 203.
The front wheel side is driven by the engine as the main drive source. Therefore, it is possible to travel as a hybrid automobile of a four wheel drive.
Further, as the conventional reduction-drive device, there is also a device as shown in FIG. 16. In the same, for simplifying explanation, the composing parts corresponding to those of FIG. 15 will be given the same reference numerals. In the motor reduction-drive device 201A of FIG. 16, the first transmission shaft 207 and the second transmission shaft 215 are coaxially disposed, and the first reduction mechanism 209A is composed with a planet gear mechanism.
Therefore, the output of the electric motor 203 is transmitted to the first transmission shaft 207, reduced at the first reduction 209A, and transmitted to the second transmission shaft 215. The torque transmission after the second transmission shaft 215 is the same as the case of FIG. 15.
However, since the first reduction mechanism 209 and 209A is installed near the electric motor 203, an attaching error of the electric motor 203 gives a direct influence to the first reduction mechanism 209 and 209A, and improvements of acoustic vibration or durability have been limited owing to occurrences of vibration or abnormal sound in the first reduction mechanism 209 and 209A (see, for example, JP-A-2001-287550).
Furthermore, as a conventional reduction-drive device, there is, for example, a device as shown in FIG. 14 (see, for example, JP-A-2003-104073). The motor reduction-drive device 1201 of FIG. 14 reduces an output of an electric motor to transmit to left and right axle shafts and drive, left and right rear wheels. The electric motor is served as a sub-drive source. At a side of front wheels, an engine such as an internal combustion is served as a main drive source, and the left and right front wheels are driven by the engine.
The reduction-drive device 1201 rotatably supports a first transmission shaft 1207 at a housing 1205 of a stationary side. The first transmission shaft 1207 has a reduction gear 1211 composing a first reduction mechanism 1209. The reduction gear 1211 is in mesh with another reduction gear 1215 of the first reduction mechanism 1209. The reduction gear 1215 is supported by a second transmission shaft 1217. The second transmission shaft 1217 is disposed in parallel to the first transmission shaft 1207, and is rotatably supported to the housing 1205.
The second transmission shaft 1217 is provided with a reduction gear 1221 composing a second reduction mechanism 1219. The reduction gear 1221 is in mesh with another reduction gear 1223 of the second reduction mechanism 1219. The reduction gear 1223 is rotatably supported relatively to a differential case 1227 of a rear differential device 1225 via a bearing 1229.
The rear differential device 1225 supports a differential gear mechanism 1231 within the differential case 1227. The differential case 1229 is rotatably supported to the housing 1205 by the bearing 1233.
Transmission and break of torque between the reduction gear 1223 and the differential case 1229 is performed by an electromagnetic clutch 1235 using multi frictional plates.
Accordingly, in case the electromagnetic clutch 1235 is under a torque transmitting condition, if driving an electric motor, a torque reduced through a first and second reduction mechanisms 1209, 1219 is transmitted to a rear differential device 1225. From the rear differential device 1225, the torque is transmitted to left and right axle shafts. By this torque, driving of an engine is helped when starting travel or ascending travel.
When the electric motor is at rest, the electromagnetic clutch 1235 is switched to a torque cutting off condition. Even if, under this switching condition, rotation at the wheel side is transmitted to the rear differential device 1225, the rotation is never transmitted to the first, second reduction mechanisms 1209, 1219 and the electric motor. Therefore, when an output of the electric motor is stopped, the first, second reduction mechanisms 1209, 1219 and the electric motor are never forcibly rotated by the rotation of the wheel side.
For getting high output in the reduction-drive device 1201, this can be in general accomplished by enlarging a scale of the electric motor.
However, there has been a problem that if building such a structure of merely carrying out the high reduction by the first and second reduction mechanisms 1209, 1219, abnormal noises easily occur in the reduction gears 1211, 1215 or the reduction gears 1221, 1223.